No, 32 bit/pixels is not related to whether the computer is 32-bit or 64-bit.
You need to know your exact processor model. The very first Celeron D processors, from June 2004 (known as "Prescott") were 32-bit. The later generation of Celeron D processors (known as "Cedar Mill") were 64-bit.
Here I found an information how you can from under Windows XP determine if your processor is 32-bit or 64-bit. Note that this is different from whether you are running a 32-bit or 64-bit operating system. You can run a 32-bit OS even if your processor is 64-bit.
However, 1,5 GB seems to be very little to run Ubuntu with a full graphical desktop. Someone suggested Lubuntu in the comments - or, if you don't need a graphics environment, you can try a minimal installation of Ubuntu Server, which has no GUI.
You can also try a completely other distribution, not any Ubuntu variant, but that is off-topic for this board.
hp d220mt (dr159p), (celeron 2ghz, 1gb (732mb useable), 82845G/GL Brookdale-G/GE (i915))
in some testing, it ran Lubuntu 18.04 LTS the best (better than Debian 10/Buster LXDE which surprised me), but I generally ignored it as it was slower than pentium M laptops, or pentium 4 desktops (which weren't sharing RAM with graphics as well as having better cpus). Lubuntu 18.04 I still use on a thinkpad t43 which has 1.5gb of RAM, but I do limit how I use it. – guiverc Feb 17 '21 at 22:04