To answer the original question generally, it depends more on time than distance. I'm basing this on surveys I've read and general statistics more than personal opinion. It turns out that when the commute each way takes more than around an hour, or even 45 minutes in some cases, that it becomes less tolerable for most people and they seek out alternatives or ways to mitigate it. So the cut-off between normal or usual and onerous is about 45 minutes to an hour.

That's mostly in reference to driving but it seems to hold up for other modes as well. I think we could extend that time at least a little for bicycling because we tend to enjoy it, which often can't be said for rush-hour driving. Seventeen miles is near the top end of that range, probably a bit beyond for most cyclists who may take an hour and a half for that distance (more with the hills). With your 12 miles on the MUP that's mitigated, it's going to be easier than 17 miles in traffic all with stop lights and hills.

I commuted for a year 10.5 miles each way, every day. That's considered a medium length commute, and frankly wasn't arduous at all after I got used to it. Over 10 to 15 starts to become a "long" commute. Mine is a wimpier 7.5 now, to me easier than driving when all things are considered. I think you could work up to that 17 mile commute, either half-commuting as has been suggested or starting with one or two days a week and building up, and eventually do it without difficulty.