For network windows shares you need to specify the uid/gid that the drive should be mounted as and/or the file and directory modes to use since Windows doesn't understand Unix users and Linux doesn't understand Windows users or permissions. Right now, the share is probably writable but everything is owned by root so no other user can do anything.
mount -t cifs -o username=winuser,rw,uid=linuxuser,gid=linuxgroup //192.168.15.10/Web /dev/fileserver
Where linuxuser and linuxgroup are both your username in Ubuntu. If you need to make the windows share writable to everyone, then you can use
,dir_mode=0777,file_mode=0666 instead of uid= and gid=. If you need some people to have access and others not to, then you can combine both of them:
mount -t cifs -o username=winuser,rw,gid=somegroup,dir_mode=0775,file_mode=0664 //192.168.15.10/Web /dev/fileserver
which will give write access to all members of
somegroup but everyone else will only have read access.