why so much swimming in silver level beginner sprint HR plan>

Hmmm....I just looked at your planned training...the runs may be on the short side at the beginning, but you do build-up to about an hour and 20 minutes by the last month.  That is more than enough for a sprint.  And the runs are a consistent 3x per week.

Assuming your are not 'new' to the sports and can do the first few weeks easily enough, these plans are more '2nd year' plans for better improved performance or if you have a strong base in another sport currently - which it appears you do from swimming.  That is why the swim's may seem 'long'...it's for improved performance.

Just for comparison sake, look at the 'couch to sprint' there is a big difference as that is the first year from no endurance plan and it's not geared for improving performance, just building up base.

If you really feel the swim is too much or you have a good enough base, then you can surely add-in/replace (or just shorten them) with another 'shorter' run during the week...that is if the 3x per week is no problem...just keep the minutes low to start on the 4rth run...this will help with more 'run durability' - but only if you have some base - don't do it if your still green....and don't do it if you're new to biking 3x per week too along with the the swim and run...training for 3 sports if you haven't before takes some getting used to also...

If you look a month or two into the plan, you will see some 'speed' sessions and a few 'bricks'...most of your runs will be in HR zone 1-2 for endurance/base.  Make sure you either go to 'blog-->planned' to see the details or the 'week or month---planned' reports with the 'show comments' checked.