Unfortunately I will not be of any help.
Although I also experience problems with file uploads my problem is related to permissions (at least according to the error log) and not hardware performance or configuration.
In addition, my instance of Bitnami's LAMP is running on AWS Lightsail. I currently use the $3.50 per month option (512 MB RAM, 1 Core Processor, 20 GB SSD, 1 TB Transfer). Mainly because I do not expect medium to heavy traffic and use for the web app.
I have deleted my previous instance and created a new instance to see if that will resolve my file upload issue. Maybe there was a config somewhere which prevented file uploading. With the previous instance to me and the @jdrios the permissions set up looked OK.
Sorry for not being able to help.