How Can I lower my Btc node's Mempool

Hi I’m mining Btc with 5 bitaxe supra. When I look at my node’s new block time sometimes block times 5 min ago and new block 2 min ago. All we know as every new block creating almost every 10 min. why my node’s new block time changing this much. my mempool is sometimes 6mb sometimes 30 mb sometimes 42 mb. How can I lower my mempool mb ?. which config I need to use or Which app I need to run ? My umbrel running just 2 apps btc node and publicpool app.

cpu 9400f
32gb ddr4 ram
2 tb nvm