First Timer: Nervous Questions!

Hi there.  Welcome to the world of triathlon

It will certainly get better with practice.  I find with swimming it is better to do more frequent workouts, rather than fewer, longer ones.  Swimming is about technique, so improving this is key.  You could research some drills that would help with this (sorry can't help any further with this - swimming is not my strong point either).

If you are wearing tri shorts you shouldn't experiance any chafing issues.  Time in the saddle will sort out any discomfort.

It often feels funny running off the bike.  I think it would be sensible to do some BRICK sessions, evenif it is only a quick 10 minute run after a ride.  Just make sure you don't overdo it by adding too much extra volume to your training program. 

Yes, I think so.  If the 15K race is a goal then you will need to keep training for it.  If you are already comfortable with this distance then there is no point cutting back.

Like I said above, to improve your technique it would be better to do more shorter workouts than one long one.  Having said this you do need to build up the distance so you are capable of swimming the 1.5K.

Which race is more important?  Will training for the triathlon limit the time you would have spent running?  In terms of the triathlon starting now would be better than waiting.  Building from 8K to 40K on the bike could be done in 10 weeks but I would be starting that process now.  Same with your swimming.

Hope some of this helps and good luck.  Keep posting any questions you have

Welcome to BT and the multisport world or...as my former running partner would say...you and your psycho friends...  

Invest in some swimming lessons.  You'll be much better served learning good technique first rather than having to unlearn it.  Learn good technique for front crawl.  It is the fastest swimming stroke because it is the most efficient swimming stroke.  (Geek alert:  "Freestyle" means you can swim any stroke, and most swimmers choose front crawl because it is the fastest.  While rare, there are times you'll see something other than front crawl in a freestyle race.)  You'll find triathletes doing everything from near-perfect front crawl to breastroke to sidestroke to dog paddle to back stroke during the race, and maybe one competitor does all of them.  

45 minutes to complete the 1500 meters is a little faster than most cutoffs, but not bad.  Keep swimming, especially with lessons, and you'll be under that time.  

Most shorter triathlons don't have changing facilities (iron distance races usually do).  The race may have a port-a-pot in transition and you could duck in there and change, but you'll generally dry off quickly after you start riding and a race in June in Wisconsin should be comfortably warm.  You can try body glide (it's like a stick of antiperspirant) where you chafe, or try different clothing.  

Your butt will toughen up the more you ride.  Consider getting a bike fit as that also makes a big difference in how long you can comfortably ride.  When the seat is at the right height, much of your weight is transferred through your legs/feet rather than your butt.  If you can sit on the seat with your feet on the ground, the seat is too low...

It's reasonable to keep running 10K as your long run as long as you have the time in your schedule.  

It's reasonable to build up to swimming 1500 yards/meters.  Rather than swim 1500 yards straight, most swim plans will have you swimming repeated shorter distances, so maybe a 300 yard warmup, 6x50 drills, 4x50 kick, 6x100 main set, 100 yard cooldown.  Why 6x100 instead of 600?  You want to reinforce good form, and the longer you swim, the more your form degrades.  Rest a little and restart with good form.  

I'd do some cross training (swimming and cycling) now even as you focus on the 15K.  BT has some beginner plans available for free.  See what the last 10 weeks of those plans look like and be ready to switch to that plan after your 15K.  

Look on the bright side.....the worst thing that can happen to you is that you'll love it. 

(I'm not kidding)

Most everyone here was where you are....now they just have a lot less time and money.

That plan seems reasonable except you're short-changing your biggest limiter...the swim.  You need to get at least 3 swims in per week...4 would be better...try not to go more than 2 days without getting in the pool.  1500 meters of open water swimming is a fair distance so you'll need to get comfortable doing 2000-2500 yd workouts by race date.

Cycling.  You'll see big improvements (comfort and endurance-wise) from just spending time in the saddle.  You'll see bigger improvements if you push the pace (within your abilities and given the length of the ride) on those rides.