I've expounded on the Whaler vs RIB issue a few times here so won't bore y'all again, that way at least. We have a 2005 13' 130 Sport. The OP was about towing a larger boat than has been discussed in the responses, but I can comment a bit on that. We have done a lot of towing in the last couple of years, since we have become more stationary cruising wise. The slip we have, and really like, has the finger pier all the way down the starboard side, so I cannot davit the boat on or off while at the dock without some hassle of moving the big boat. We use the Whaler a lot when in port during the nice weather, so towing it was the way to go for us. We use the ocean a lot to get where we like to go, as well as notoriously choppy Neuse River/ Pamlico Sound.
First of all, the 13 tows beautifully in all kinds of sea conditions (well we haven't tried it in 10 footers yet, but multiple times in some miserable 3-6' steep choppy crud in high winds), so I would expect a 15 or larger to do even better. You need to get the small boat positioned correctly, but in my case, since we go 9 knots, not precisely. The logistic hassles leaving and coming into the dock or anchor are moderately more of a PITA than putting the thing on and off the boat deck, but not a lot more. The Whaler being a heavy boat, it is less "wieldy" to back on the chocks.
However, if we were back to full time long distance cruising, I would, as before, far prefer having a boat on the boat deck than towing it around. It definitely adds complexity to getting in and out of a new marina and slip (you essentially have a much longer boat now, with one end that wiggles around a bit), and often times will cost you more in slip fees and restrict what sort of slip you can be allowed in. Going from anchorage to anchorage, it's not so bad, save for when you are having to wait for a bridge to open, which can be another big PITA with a tow. Fendering the boat off the swim platform can be a challenge in rough weather, especially when various forces may be slamming the tender up against the big boat, with one going up and the other down at the same time;yes, it happens even when they are tied together. and if you let it drift off away from the big boat under those conditions it just gets that much more of a head start. We considered going to a bigger, towed boat since we enjoy exploring around so much and a little more space and freeboard would be nice, but have scratched that idea given the above. But that's just us. We like the Edgewaters a lot in that mid teens size range, moreso that the Whalers; Scout had a nice boat too, may still.
I do have to comment that a 13' Whaler will hold a LOT more stuff than a similarly sized RIB, forget the weight capacities. We went to MIBS one year with the thought of changing to save some weight, etc. The Whaler is what came with the boat so at that point we weren't married to it. We looked at dozens of RIBS from every mfr and none came close in interior room. Since the tender is the family car for us when we stay on moorings for a large part of the season, being able to haul guest luggage, groceries, supplies, people and stuff is a big consideration. Its also a very easy platform to fish from, and putting a hook or a gaff in the side just requires gel coat.