It is. With 10k MRR it represents 0.15% of the revenue. Having the whole backend costing that much for a company selling web apps is like it’s costing zero.
I don't know what you value your time or opportunity cost as... but the $10/mo doesn't need to save very many minutes of your time deferring dealing with a resource constraint or add too much reliability to pay off.
If resource limitations end up upsetting one end user, that costs more than $10.
And most VPSs allow increasing memory with a click of a button and a reboot.