The H on the left indicates HW offload is active for that port. You can toggle it on and off with the hw-offload=yes/no option. If you set hw-offload to yes RouterOS still makes a decision about whether or not your configuration is viable for hw-offlaod and that is represented by the H to the left.
An example, my RB750Gr3 has crap for a switch chip so even though I've set hw-offload=yes for my ports they largely indicate no acceleration because I have enabled MST and connected the ports to a Cisco switch (trunk links).
By separating ether15 out into another bridge it seems you've passed the conditions of hw-offload as indicated by your /interface bridge port print command. The last thing, regardless of old fashioned switch chip configuration or the new VLAN aware bridging any layer 3 (inter-VLAN) routing is always performed by the CPU and is therefore limited by the CPU.
Now your original post, is the question how to make a port an access port for a VLAN other than the bridge's PVID (untagged at the bridge)? If so, have a look at the example below. We'll create an environment with 3 VLANs, 1 will be used for untagged traffic on the bridge (default behavior, shouldn't be used for customer traffic per best practices), 11 will be for one building and 12 for a second building. VLAN11 will be 10.1.11.0/24 and VLAN12 will be 10.1.12.0/24. The ether2 interface will be an access port (untagged) for VLAN11, ether3 will be an access port (untagged) for VLAN12 and ether4 will be a trunk (Cisco) with VLAN1 as the untagged VLAN and VLANs 11 and 12 tagged.
/interface bridge add name=br1 igmp-snooping=no vlan-filtering=no
/interface bridge port add bridge=br1 hw=yes interface=ether2 pvid=11
/interface bridge port add bridge=br1 hw=yes interface=ether3 pvid=12
/interface bridge port add bridge=br1 hw=yes interface=ether4 pvid=1
/interface bridge vlan add bridge=br1 vlan-ids=1 untagged=br1,ether4
/interface bridge vlan add bridge=br1 vlan-ids=11 untagged=ether2 tagged=br1,ether4
/interface bridge vlan add bridge=br1 vlan-ids=12 untagged=ether3 tagged=br1,ether4
/interface vlan add interface=br1 vlan-id=11 name=br1-vlan11
/interface vlan add interface=br1 vlan-id=12 name=br1-vlan12
/ip address add interface=br1-vlan11 address=10.1.11.254/24
/ip address add interface=br1-vlan12 address=10.1.12.254/24
/interface bridge set br1 vlan-filtering=yes
In other words, you really only need 1 bridge with multiple VLANs not a VLAN per bridge. Their was a legacy way to do software only VLANs by having a bridge for each VLAN but that is long dead with the 6.41rc+ bridges thankfully.