Can I make the system reserve for partitions smaller?

mkfs.ex4 to create a linux ext4 file system

When you use mkfs.ext4 you will create a new file system (and the data in the partition will be lost). You must backup all data, that you cannot afford to lose, before doing it.

You can use the option -m to specify the reserved percentage, for example to get 3%,

sudo mkfs.ex4 -m 3 /dev/sdxn

where x is the device letter and n is partition number, for example /dev/sda1.

From man mkfs.ex4

   -m reserved-blocks-percentage
          Specify the percentage of the filesystem blocks reserved for the
          super-user.   This  avoids  fragmentation, and allows root-owned
          daemons, such as syslogd(8), to continue to  function  correctly
          after non-privileged processes are prevented from writing to the
          filesystem.  The default percentage is 5%.

tune2fs to modify a linux ext4 file system

When you use tune2fs you will modify an existing file system (and the data in the partition should be preserved). But you should backup all data, that you cannot afford to lose, before doing it.

You can use the option -m to specify the reserved percentage, for example to get 3%,

sudo tune2fs -m 3 /dev/sdxn

where x is the device letter and n is partition number, for example /dev/sda1.