With SDHC card:
Max read speed is going to be right about 80MB/Sec.
Access time is slow compared to HD or SSD.
Conventional HDs sustain ~180+MB/Sec.
SSDs sustain ~520MB/Sec.
If you use much disk-streaming polyphony (from Kontakt or similar), it's just not fast enough to keep up.
If you can add a m.2 SSD to your laptop, that would be a far better solution.
If not, your best compromise solution would be to add a large SSD.
Split the large SSD into two partitions (OS and Audio).
This isn't ideal, but at least you'd have 500+MB/Sec (total) for all duties.