I'd recommend setting up some alerts on your current server (Standard_D8s_v3) to monitor the usage of RAM and CPU. Realistically speaking, if you are not hitting a consistent 80-90% usage of your specs then you really don't need to upsize.
Create recommended alert rules
Please understand that there is a cost associated to this, but will help you understand if you need the upgrade. You can also disable these at a later time.
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