You need to reduce as many variables as possible, so get cloudflare out of the way for these tests. You should be testing directly to your server.
First, run some ping tests to both server IP addresses using a tool like this: https://www.cdnperf.com/tools/cdn-latency-benchmark
You can run some pings and traceroutes FROM each of the VPS servers as well. This will give you some idea of there is slowness in the network.
Check to see if your host has a looking glass and test IP's and if those are any different than your IP.
For any VPS I would want to make sure that the server you are sharing or network segment is not overloaded by a noisy neighbor or that the VPS overall is simply oversubscribed for CPU/bandwidth/disk whatever with too many other people running on it.
Try running some benchmarks, maybe a script like bench.sh (check it over carefully to make sure it is safe as I have not.)
https://bench.sh/
https://www.vpsserver.com/community/tutorials/3938/one-click-test-server-performance-script/
That and another option are discussed here: http://www.servermom.org/quick-test-server-performance/2267/
Here are some tests you can do without a script:
https://haydenjames.io/web-host-doesnt-want-read-benchmark-vps/
ONLY AFTER verifying you have a nice, fast, clean VPS should you then put cloudflare on and THEN try to determine if this is where your problem actually is. If the servers are great without CF and then the problem shows up when you test WITH CF... then you know you found your problem.... CF (unlikely).
I am guessing that your slower VPS is just going to turn out to be slower. Maybe CPU, maybe network. If you can get some conclusive data, ask your host about it. Perhaps they can put you on a faster box. But beware... that may just be temporary until you get more bad neighbors!
Please mark this as a solution or upvote if this is helpful. Thanks!