Tax implications for withdrawing from rolled over traditional IRA to a Roth IRA?

So I (31 y/o) recently learned I apparently had a 401k at a previous part time job, and it was rolled over into a traditional IRA. I already have a Roth IRA, and my understanding is you cannot contribute more than $7,500 per year across all IRAs. I'd like to withdraw the money from the trad IRA and contribute it to my existing Roth. It's not that much money, less than $1,500. What are the tax implications for doing this? Do I pay taxes at the time of withdrawal, or when filing taxes next year? Is there any reason I should not go ahead with this? Thanks for any advice!