Average is probably less than 15 actually. 15 is somewhat of an exaggeration.
Usually I start tempting the Squamish chum around October 15, and I'll fish for them until early December. Best time throughout the season... well, there isn't a best time really, you can catch chrome fish all the way until December. Lower Squamish fishing result is dictated by the tide. High tide means more fresh fish. Chrome chum are there, but not as many as most think. You might come across one out of every 20 or 30 fish.
Last year we did ok, here are some photos to get things warmed up.
Chrome chum number oneChrome chum number twoA couple of notes regarding fishing for them. Squamish chum are eager biters, as long as you have the colours right. Last year, changing from chartreuse to yellow meant going from 2 hours of dry float to fish on every drift. Short floating works totally fine here, as long as you find a stretch that has a good drift. 12 to 18 inch leader, total depth about 3 to 4 feet from float to hook. Don't wade out too much, fish are right in front of you. Start by casting close to shore. Those are not underwater logs, but resting fish.
Good luck.