If you're experiencing NuGet repository performance problems in Nexus Repo 3 there are number of things you can check.
Make sure your instance is meeting our system requirements outlined here:
Be sure to upgrade to the latest version, performance improvements have been made in newer versions.
Use NuGet v3 Protocol
If you are running Nexus Repo 3.25 or higher configure NuGet clients to retrieve components using the v3 version URL's, these are much more efficient than the old style v2 URL's.
Excessive Memory Consumption in 3.23.0 and Higher
To better support package installation via Powershell we fixed an issue in 3.23.0 where multiple versions of the same package could be identified as the "latest" (NEXUS-20349). That fix can cause increased memory consumption when old style NuGet v2 URL's are used for package retrieval.
If you can't switch to NuGet v3 and don't rely on Powershell you can disable this fix by adding the following line to $workdir/etc/nexus.properties