Just saw this on new posts. My kids are farther apart than that, but I can tell you my experiences breastfeeding, perhaps as a little cautionary tale. I got pregnant with DS2 when DS1 was about 19 months old (lactational amenorrhea is great!). My supply decreased, nursing became incredibly painful (imagine being stabbed in the nipple with a stiletto knife every time baby nurses), then supply dwindled to almost nothing. It was very painful nursing through that pregnancy (I kept it up for bonding and because I knew that tandeming would be beneficial for the kids' relationship), DS1 was certainly not going to get all his nourishment from milk because I wasn't producing an adequate volume by about month 4 of the pregnancy, so I would be hesitant to do this with a baby when you hope to do exclusive breastfeeding for at least 6 months (as opposed to the other EBF, extended breastfeeding, which is also a possible goal with closely spaced nurslings). Tandem nursing might also result in the closeness you are perhaps desiring without having the kids born less than 18 months apart -- it was a good experience for me (though I never expected I would do it prior to the second pregnancy and DS1 not weaning when the milk supply went down).
I will grant you, I was 35 when I was pregnant the second time, so maybe this decrease in supply would be less of an issue for a younger woman. However, I would be completely unwilling to sacrifice my infant baby's milk supply just to have close child spacing. That milk is so important for your LO's immune function, brain growth, gut flora colonization, hormones, and things we probably don't even realize yet. So, I would not cut down on nursing sessions or length, and I wouldn't want to get pregnant again before baby was at least a year old, just because of the milk supply issue.
Also, in many cultures where extended breastfeeding is the norm, child spacing seems to be naturally about 2 1/2 or 3 years apart, indicating that a woman's body perhaps likes to devote its resources to the child on the ground before starting to sustain a second babe in utero. I think it's nice for the mother's body to rest and heal fully from the stresses of one pregnancy, rebuild stores of calcium, iron, other nutrients that have been depleted by that pregnancy before hurtling into another one. It's a luxury only to have one baby who needs your attention. A 3 year old has some (small) concept of what "I'll be with you in a minute" means, and a 16 month old does not (and they can get themselves in trouble faster than you can say "clogged toilet," "5 lbs. of rice all over the floor," or "faceplant into the fireplace.") For your health and sanity, I'd advocate for more distance unless you have a pressing reason to go for closer spacing (like, you know you will have surgery to remove your uterus and the ginormous fibroid tumor as soon as the last baby is born, and you know you need to get this done in the next two years, something like that.)
That's my unsolicited two cents, anyway.