Things in the config which point to unreachable or slow (e.g. work VPN) network drives, as well as antivirus are often the cause of slow startup, but there are other possibilities.
Some others are discussed in these threads, which are a good place to look for things that might be relevant to your system:
If nothing in those seems relevant, you could try recording a Process Monitor log of what happens when you launch Opus, which may reveal which resources it is trying to access that are so much slower than normal, or which components on the system are slowing things down: