On Feb. 8, I brewed.............By the 13th, the bubbler had slowed significantly and the SG was 1.015 so we racked to the secondary fermenter. Nothing happened until today, Feb 18, .............
It will likely be fine. If I understand the timing correctly, a day-time brew on the 8th would mean pitching yeast that PM at best. Under ideal conditions, fermenting activity might have started that night, but probably next day in earnest? So it ferm'd on the 9th thru 13th for only five days. Every beer/yeast is different, but 7-10 days is preferred.
While the bulk of the active Sugar-Eating phase of the primary ferm had passed, I suspect the more complex sugars were still being eaten, and the yeast still had clean-up work to do. There were likely lots of yeast in suspension still eating and cleaning that went to the secondary. The slight infusion of oxygen from the transfer probably aided in their restart, (hence the new activity and surface evidence), but their numbers are drastically fewer now after racking off the yeast cake. Finishing fermentation will take longer with fewer yeast cells doing the job.
I would let it set a while to ensure the remaining sugars are consumed and the yeast has time to process the diacetyl. Rouse it gently to keep yeast up in suspension. If you used an English yeast that creates a bit more diacetyl, you'll want to be patient on the secondary.
Before bottling, check gravity and taste it for a buttery flavor and/or a slick coating sensation from excess diacetyl. If present, wait longer.
