will you see benefits to upgrading to orbi AX? Sure.
Will they be worth the cost? That depends on a lot of things.
1500 sqft isn't a huge space so you're not looking for coverage.
The 50 series was also the higher performing of the orbi versions so you're on the best AC system orbi had/has.
Are you needing faster speeds or concurrent broadcasting?
do you have many AX devices?
You might see a little bump in speeds for your AC devices.
I switched from AC to AX and seen a little difference in speed on my AC devices but I didn't see enough to fully justify it (don't tell my wife). Problem is that most of my devices that max out speeds (my server) is hardwired in. The rest mainly streaming/browse//game and don't really need max speeds. They just need consistent speeds that are high enough to do them. For instance, you'd only need 20-40mbps to stream 4k is good quality.
If it was me and the 50 series was meeting your needs still, I'd hold off for second generation AX technology or wifi 6E. The first generations of wifi standards always tend to have a few bugs/performance issues
