#JavaScript, Z (90) bytes

for(i=65,b=66;i<91;++i,b=b<90?++b:65)console.log(Array(14).join(String.fromCharCode(i,b)))

To learn:

var start = 65,
 end = 90;
for (var i = start, b = i+1; i <= end; ++i) {
 var chars = String.fromCharCode(i, b);
 /* repeat chars 14 times */
 console.log(Array(14).join(chars));
}

JavaScript, Z (90) bytes

for(i=65,b=66;i<91;++i,b=b<90?++b:65)console.log(Array(14).join(String.fromCharCode(i,b)))

To learn:

var start = 65,
 end = 90;
for (var i = start, b = i+1; i <= end; ++i) {
 var chars = String.fromCharCode(i, b);
 /* repeat chars 14 times */
 console.log(Array(14).join(chars));
}

#JavaScript, Z (90) bytes

for(i=65,b=66;i<91;i++,b=b<90?++b:65)console.log(Array(14).join(String.fromCharCode(i,b)))

#JavaScript, Z (90) bytes

for(i=65,b=66;i<91;++i,b=b<90?++b:65)console.log(Array(14).join(String.fromCharCode(i,b)))

To learn:

var start = 65,
 end = 90;
for (var i = start, b = i+1; i <= end; ++i) {
 var chars = String.fromCharCode(i, b);
 /* repeat chars 14 times */
 console.log(Array(14).join(chars));
}

#JavaScript, Z bytes

for(i=65,b=66;i<91;i++,b=b<90?++b:65)console.log(Array(14).join(String.fromCharCode(i,b)))

Using bad pratices, but shortest.

#JavaScript, Z (90) bytes

for(i=65,b=66;i<91;i++,b=b<90?++b:65)console.log(Array(14).join(String.fromCharCode(i,b)))