Yes, and even a couple more since CU15 has been out of support for a good while now (June 16, 2020) and other security updates have been released in the mean time as well.
Update to CU19 as soon as possible and then apply the security updates.
Once CU20 comes out, make a plan to update to remain supported; Only the last 2 CUs are supported, so once CU22 comes out, CU20 is no longer supported.