Most people use Flickr or some other hosting site as your uploads will eventually exceed your limits. For Flickr you copy/paste the bb code right into your post.
I use PS Elements and to resize you do it in the edit window. Image, Resize, input your pixels for the wide edge and save.
You don't need to reduce the image size (pixel dimensions/image resolution).
What you need to do is reduce the file size.
As long as the file size is no more than 2 Mb you should be OK.
Though I've not found anywhere on TPF that specifically states the site file size limit, other members have said they think it is about 4 Mb.
The previous site software had a 2.2 Mb file size limit.
File size is reduced by changing the JPEG Quality setting value when the image is Saved.
But as mentioned if a image file is hosted elsewhere on the Internet we can use the Media icon in the text editor to put the URL of an image in our post and not have a file size limit.
Not all camera make photos that have the same aspect ratio.
But 1500 x 800 is an odd 1.875 aspect ratio.
35mm (135 format) DSLR cameras (full frame and APS-C) make photos that have a 3:2 (1.5:1) aspect ratio.
Cameras with four/thirds size image sensors have a 4:3 (1.3:1) aspect ratio.
And a lot of video is made with a 16:9 (1.78:1) aspect ratio.