What price did you pay for them?
Hard to make the call without knowing what you paid.
At $450 (Adorama's current sale price) for the R-26PF, if you paid the current Amazon price of $438 for the R-15PM, it is a no-brainer, but we don't know the open box price you paid at Best Buy.
With a 3 year old, I would be inclined towards the towers from a mini-Godzilla perspective - not saying it would be much harder to push over the towers, but at least it will all fall in the same direction in one piece.
OTOH, if you would use the 15's on a shelf, he probably could not get to them!
The 15's have a rear facing port which means you need to leave some room behind them for the port to "breathe".
If you are buying stands for the monitors, that is a $ point in favor of the towers.
Of course only you know what is right for you.
How do you like the 15? Does it leave you short on bass?
If so, I'd want to try the 26 and see if you could avoid the sub and keep good karma with your neighbors (assuming they are respectful neighbors).
Yepimonfire's comments about what type of music you listen to are important. Very few traditional instruments go below 40Hz (26 is spec'ed to 38Hz, 15 to 62Hz), but if you listen to some of the current electronic music, you ma be left wanting more bass.
Are you streaming from your phone? If so, find an app for tone control/EQ.
Also, note that the 15's appear to be a passive design, having 2 x 50 Watt amps for the two channels while the 26 appears active with 2 X 20W amps for the L&R tweeters and 2 X 110W amps for the L&R woofers.
Unfortunately, we have little idea of whether Klipsch took full advantage of having an active crossover for the 26.
I paid $220 for the 15's at BestBuy. These were a namesake Open Box, someone had only opened the tape leaving the speakers and accessories box unopened. That day 15's were retailing $297 at BBY, so $220 for OB. I am sure they would have corrected the OB price now that 15's are back to the retail price of $499
I was planning to use a speaker stand for the 15's, but the mini-Godzilla perspective stands true, so definitely towers for that reason.
I am coming from a 10yr old Sony Sound Bar HT CT 100, so the 15's are definitely a treat for my ear with distinct left and right channels. But 15's lack bass that I want.
I want to give 26's a try, but if they are too loud or take too much real estate(both on the floor or visually), I would want to keep the 15's with a sub. My cousin has a 15's and 12" Sub setup, and I was impressed with its sound.
I was well on a path for the 15's and 10" sub, but the tempting price of $450 for 26's caught me.
Only after trying 26's I can be sure of what I want to keep.
I mostly listen to Bollywood music, electronic, alternative rock and some Indian classical, so bass is a must. One good thing about 26's is they have 100V-120V / 220-240V selectable power supply, so they should work fine in any country if I happen to relocate.
Thank you for the technical insights that I was never aware of.
