Are LRDI sectionals way too hard or am i just too bad in it???

Nopes, some sectionals are way tougher.

Some are super easy some are super hard but coaching institutes always have lower quality questions compared to CAT which has some beautifully crafted questions and might test concepts never asked before so it's almost impossible to predict LRDI performance from mocks.

When a number is divided by 3, 4, 6, 15 and 20, the remainder in each case is 1. Also, the number is the greatest 3-digit number. The sum of the digits of the number is:

K(lcm of 3,4,6,15,20) + s , where s is the common remainder (ie 1) K*60 +1 K=0,1,2,3 and so on. So when k=16 we get the highest 3 digit no. Ie - 960+1= 961 So sum of digits = 16

You can crack it by taking 980,960 or 940and adding 1 in the end as these values are the only ones that are divisible by 20 in 900 range, its easier just to divide using calc and check

How is dashcat 15? is it similar to dashcat 14?

to me it was harder than 14 as I have scored only 45 against 55

I want to prepare for CAT free how can I get concept videos and resources

There are no free lunches my boy. Price of cracku is just 19k which is very less as compared to TIME, CL etc. my advice to you is just enroll for cracku.