It is possible to grow the hard drive in Virtual Box, as you had already found out. After that you will have to partition the drive with gparted
from a live session and maybe join partitions. This has been adressed before. See the following questions:
For your layout it means you would have to remove your swap partition (sda2
and sda5
) before you can join the adjacent space.
All of these procedures take considerable time and will put you data at risk. You will have to make a backup first. Because you then would already have a backup it would be much much faster to just create a new virtual hard drive where you can restore your backup and keep going.
You can even create a new virtual drive, attach it to your existing virtual machine, and copy your data over.
A new hard drive should be made a dynamically allocated disk (this is the default for new drives in Virtual Box). This means they will grow on demand up to the maximum size you gave it. The actual physical size will be much lower. So when creating a 100 GB dynamically allocated drive it may only use 8 GB of physical space or less.
This will enable you to be generous with space. You present 15 GB is rather small and may soon become too small when using it.