Upgrade from SDL Trados Studio 2015 Freelance Plus to SDL Trados Studio 2021 Freelance Plus

Hello,
I am planning to upgrade from SDL Trados Studio 2015 Freelance Plus to SDL Trados Studio 2021 Freelance Plus. I saw there were interesting offers for Black Friday but I still need to upgrade my two computers to Windows 10 before purchasing the Trados 2021 upgrade.


I have two questions:

Can I buy the upgrade now and activate it later, when my computers will be fully operational? I will start with my desktop computer first and then, I will upgrade my laptop (not both at the same time).
Can I still use SDL Trados Studio 2015 Freelance Plus even if I bought the upgrade (as long as I don't activate it on my computers).


Thank you very much

Laura