Will a low credit score and an account in collections prevent enlisting?

Will it stop you from enlisting? No. If you have dependants, you'll have to have a dependency waiver though (which would amount to the commander doing an interview to ensure you will functionally be able to provide for your dependants).

When you enlist, you'll fill out a Monthly Financial Statement (DA 3072-2) which will include all liabilities against your military pay. As long as the debt isn't for child support and the debts won't exceed your income after expenses, you shouldn't have too much of an issue.

Where you might have an issue is with the 15Q MOS. An Air Traffic Control Operator requires a SECRET clearance. Having a debt won't automatically prevent you from getting a clearance, however if there are patterns of irresponsible fiscal behavior, the debt is excessive, attempts weren't made to address indebtedness, etc. THAT could impact you.

If it's a case of "I got into debt, got my act together and am paying it off now", that will likely not have an impact at all, especially if it's an isolated issue and you haven't had any problems since addressing it.
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* USAREC Regulation 601-210 (Enlistment & Accessions Processing) - https://recruiting.army.mil/Portals/15/Documents/Forms%20and%20Pubs/Regulations/UR%20601-210_1.pdf

It certainly won't boost your chances. What may delay you is the Collections account as this MAY have you viewed as a security risk. But, the only way to fully know for sure is to speak with a Recruiter. While I can't find if the MOS 15Q requires a clearance, pretty much everyone that joins ends up going thru a background security clearance check when they come into the Service.

Having a low credit score alone isn't a major hurdle but having an active collections action against you would be a potential red flag. Speak to your recruiter and they will help cut the red tape and will also help you make plans for next steps. It will need more action on your part than theirs to clear this up but they are the ones who can help you know what direction to head. Good luck.