Yeah I don't think it's hEX CPU either, it can do more than 3Mb/s
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Are you setting the APN to something specific, or is "Use Network APN" checked? You should make sure your APN is set to correctly for your carrier. If "Use Network APN" is checked... it's possible that the Mikrotik is using a different APN than than main/customer APN (e.g. some "admin" ones for stuff like over-the-air modem firmware, which might be slower than the "real" APN). And, Windows may be smart about setting this based on carrier...but the Mikrotik looks at the SIM card, or what's set in the APN profile (if Use Network APN is uncheck).
If that doesn't work...
It a bit more complex, but you can try setting "passthrough mode" on the LTE device to a non-bridge ethernet port, then plug your laptop into that passthrough port. You may have to remove one of your ports from bridge to do it. What this will do is bridge to modem to your laptop, it be curious to know what speed the passthrough mode is getting (e.g. hotspot -> Mikrotik (with LTE passthrough port set) -> Ethernet to PC). If this got more speed, then we kinda know the TTL isn't doing anything.