Or you may look at the PDS/MSDS of the engine oil....sometimes it is indicated if it is a Group 1-3 (Mineral) or Group 4-5 (Synthetic) base oils...

The SAE viscosity is not the basis for the type of blend rather it's the base oil used....

I prefer using "mineral + regular oil changes" than "synthetic + wait until 10k or 1-2 yrs before oil change even with dirt circulating inside the engine".....there's a bigger possibility of dirt becoming lumps with synthetics than minerals due to longer oil change intervals....