Esp-wroom-32 16mb flash, spiffs partition

When i use the default 16MB flash partition table:

Name, Type, SubType, Offset, Size, Flags

nvs, data, nvs, 0x9000, 0x5000,
otadata, data, ota, 0xe000, 0x2000,
app0, app, ota_0, 0x10000, 0x640000,
app1, app, ota_1, 0x650000,0x640000,
eeprom, data, 0x99, 0xc90000,0x1000,
spiffs, data, spiffs, 0xc91000,0x36F000,

With my esp32, the file openings and readings are very slow for some reason. Even with the default 4MB partition, the 16MB esp32 is reading the files from SPIFFS very very slowly. But if i use the 4mb dev board with the default 4mb partition table my sketch is working fine. What am i doing wrong? If i create a fat file system on the 16mb one, i can not upload my data folder to the flash.