Is it possible download macOS 10.15

Yes, you can download macOS 10.15 (Catalina) from here -0> How to download and install macOS - Apple Support

But first check to see if your Mac is compatible with Catalina - here is a list of compatible Macs:

macOS Catalina is compatible with these computers - Apple Support

If your Mac is compatible with Catalina, and you upgrade to it,

• 32-bit applications will stop working
• iTunes will go away, replaced by separate applications: What happened to iTunes? - Apple Support