Upgrading to creative suite with Adobe stock— Will I lose Adobe stock credits I’ve accumulated?

There is no creative cloud subscription with stock included, except if you have a Teams or Enterprise subscription. Those subscriptions are running under the labe Creative Cloud Pro or similar and include unlimited stock access. There are certain advantages to this, there are also disadvantages to this formula. But generally speaking, the subscriptions are more for big companies with many stock asset requirements. 

As for the momement, I suppose you are interested in an Adobe creative cloud all apps individual plan, and there, Adobe stock is a separated plan. That will mean to keep your current stock plan, and the issue with accumulated stock assets is not present. 

However, if you are unsure about your exact situation, you should contact Adobe customer care. Adobe customer care can be contacted by beginning a secure chat session at https://helpx.adobe.com/contact.html?rghtup=autoOpen. Pop-up blockers need to be disabled, you need to accept cookies! If the chat window fails to open, or is non-responsive, use a different device and/or browser to start the interaction.

For support via Twitter:
https://twitter.com/AdobeCare

(see also here: https://community.adobe.com/t5/creative-cloud-services/how-to-contact-adobe-support/td-p/11875703 or here
https://community.adobe.com/t5/account-payment-plan/how-to-contact-adobe-support/td-p/11843852)

Important: Adobe does NOT contact you unsolicited by e-mail or direct message. If you get contacted by direct message from a person, claiming to be an Adobe employee, look at that profile and check if they bear the “Adobe Employee” marking under their name. Adobe support does not use Skype to give you support.
If in doubt, ask the forum.

I have read previously in this forum that you must contact an Adobe rep directly to arrange for existing credits to be transferred from one Stock subscription to another subscription type.