Source: https://xkcd.com/3172/

More context: https://www.explainxkcd.com/wiki/index.php/3172:_Fifteen_Years

I’ve copied some of it below, but I didn’t go in and add all the links:

Randall’s then-fiancée (now wife) was diagnosed with cancer in late 2010. This is a matter he has discussed in the comic multiple times before, with Randall being depicted as Cueball and his wife as Megan. At this comic’s release, it had been 15 years since her diagnosis and treatments.

This comic continues previous comics in the series – 1141: Two Years, 1928: Seven Years, and 2386: Ten Years – the initial parts of which are shown in the first 20 panels, which are grayed-out. These take us through the initial diagnosis and inability to imagine what future might be, into concerns about it potentially recurring, and up to enjoying ten years of life together that they weren’t sure they would have.

After some new panels marking more significant non-cancer-related events from the most recent five years of their life, Megan announces some potentially concerning-sounding symptoms she’s experiencing. However, the punchline is that these are just the signs of growing old, which Cueball is experiencing too. This is good news, considering the serious medical scares they lived through.

The title text continues that ending with a play on a common conversation topic. Normally someone rhetorically asks “Want to feel old?” and then follows it with a description of a difference the conversants have with the younger generation, or how long it’s been since some significant event they both experienced, as Randall has done in several previous comics. This is meant to make the other person feel bad about their age. In this case, though, the question is taken literally, with a simple “Yes” response to indicate that feeling old is better than being dead and they are happy to be alive and to have had the time they have.

The finality of this new installment suggests that it may be the last in the series, as it is solely related to Randall’s wife’s recovery from cancer.