Same here, I thought it was because I replaced the battery and it was problematic.... but reading this topic and these replies I assume this is a bigger problem. my Mac is the same, MacBook Pro (Retina, 13-inch, Early 2015) 2,7 GHz 2‑core processor Intel Core i5 8 GB 1867 MHz DDR3 Intel Iris Graphics 6100 1536 MB on Catalina it was very fast and reliable... now, a lot of lagging and getting the rainbow clock a lot of times... I hope Apple looks back to those "old MacBooks"