The answer to your question depends largely on four factors.
- The maxmium Wireguard throughput of your VPS, measured in Mbit/s (known only by your VPS provider, if at all)
- whether your VPS provider's internet connection does support that bandwidth, measured in Mbit/s ((known only by your VPS provider)
- whether your own ISP supports that bandwidth, measured in Mbit/s (known only by you or by your ISP's plan)
- the accumulated peak and average download speed by your handful of clients, measured in Mbit/s, which in turn depends on whether your VPS will handle all of your internet traffic or just DNS (known only by you, if at all)
Overall maximum throughput will be limited by the lowest value of the above.
If you are connecting to your VPS instance for DNS exclusively, then it is highly likely it will be sufficient.
If you are routing all traffic through it, you'd have to check the numbers.
None of the above is related to Pi-hole.