PostgreSQL 12 VS PostgreSQL 15

Hi Experts,

I am doing performance testing on Aurora PostgreSQL version 12, 15 using
pgbench. I see the performance is low in 15 compared to 12.

Below is the hardware configuration:

r6g.large
16 GB of RAM
2 vcpu

Below is the command used to initialize the tables: (I have used the
pgbench of 15 version to generate the partitioned tables as we have more
partitioned tables).

./pgbench --initialize --scale=1000 --partition-method=range
--partitions=30 -h <>.rds.amazonaws.com -U postgres -d postgres

For PostgreSQL 15:

./pgbench --client=16 --time=900
--host=<>.rds.amazonaws.com -U postgres -d postgres
pgbench (15.3)
transaction type: <builtin: TPC-B (sort of)>
scaling factor: 1000
partition method: range
partitions: 30
query mode: simple
number of clients: 16
number of threads: 1
maximum number of tries: 1
duration: 900 s
number of transactions actually processed: 691414
number of failed transactions: 0 (0.000%)
latency average = 20.824 ms
initial connection time = 151.272 ms
*tps = 768.337953 (without initial connection time)*
For PostgreSQL 12:

./pgbench --client=16 --time=900
--host=<>.rds.amazonaws.com -U sa -d postgres
pgbench (15.3, server 12.11)
transaction type: <builtin: TPC-B (sort of)>
scaling factor: 1000
partition method: range
partitions: 30
query mode: simple
number of clients: 16
number of threads: 1
maximum number of tries: 1
duration: 900 s
number of transactions actually processed: 863125
number of failed transactions: 0 (0.000%)
latency average = 16.681 ms
initial connection time = 146.719 ms
*tps = 959.153959 (without initial connection time)*

I did testing multiple times with different connections but still the same.

Thanks
Srinivas