Hi Tom, Good the hear that you have Linux Mint 19.1 running OK.
From reading your e-mail it appears to me that you have just "copied" the .iso image onto the SD-Card and later copied it to the 500GB USB drive. Thus you are booting up the squashed file system of the Linux Mint Live iso file.
If this is the case then you will be taking a performance hit as with the squashed file system you need to decompress the files before they can be executed. You might like to consider a $70 investment at PBTech for a 2.5 inch Solid State 240GB<https://www.pbtech.co.nz/product/HDDKIN3644174/Kingston-A400-240GB-25-SATA3-7mm-Internal-Solid-St> Sata disk drive. You could remove the current drive in your Toshia laptop and put in this SSD. You would then boot a USB drive or CDROM drive with the Linux Mint Live distro on it and "install" Linux Mint onto the SSD. After that you would then be booting a SSD drive that's about 10 x faster than a mechanical drive, and the files Linux loads into RAM do not require decompression. With regard to...
Mint has got a swapFILE in the root directory - pretty hard on the SD-card.
... with 6GB of RAM on your Toshiba, then its highly likely that under normal use you have sufficient RAM at all times and Linux never actually needs to go out and make use of the swapfile. If you only have 2GB's of RAM on a system running Linux Mint, then you can expect a system to slow down due to the need to do lots of swapping. cheers, Ian.