The reason for the slow network performance?

Question

Computer networks

Good afternoon, dear Habr experts. I am a beginner network engineer. There was such a question, there is a Mikrotik CRS125-24G-1S-2HnD. Unifi Controller(Cloud Key) is connected to it. On Mikrotik, /21 subnets are distributed. All in one vlan by default. There are about 30 Unifi hotspots. Users are mostly wireless. Configured openvpn to connect remote employees. The Internet for wired and wireless users began to work slowly. What could be the reason?
1) In a weak router?
2) Will replacing with FortiGate 60E help?
3) Will division into vlans help?

Answer 1

CRS125 is not a router, hence the problems. Set the router to at least hEX

Answer 2

4) will the increase in speed from the provider help?
Outside business hours, internet speed is normalized

Answer 3

How busy is the Internet channel?
How busy is the CPU and memory of Mikrotik during the drawdown?
Why exactly fortigate, when just mikrotik Hex is enough, as already indicated?)