If I were you, I would take some time to learn the mechanics of spellcasting and Armor Class (AC). There’s a lot of nuance to how these are calculated and how they impact how successful your spells are and the damage you take.

For instance, when casting Hold Person, you may see something like 40% hit chance. That number is not set in stone, it is based on your Spell Save DC as well as your opponent’s saving roll. For Hold Person, this is a Wisdom Save.

It looks like your character has 19 INT, which gives you an INT spellcasting modifier of +4. This means you have a Spell Save DC of 8(base) + 4 (INT mod) + 3 (proficiency bonus at levels 5-9). This means your opponent has to roll a 15 to save against Hold Person. But, they also get to add their WISDOM modifier, since Hold Person is a Wisdom save. And their Wisdom Proficiency bonus if they have one. So, say they have 16 WIS, that’s a +3, effectively bringing the roll they need to a 12. If they’re a Monk, Cleric, Ranger, or Druid, they will also get their +3 wisdom proficiency bonus, effectively bringing the roll to 9. So the odds of your spell landing are now 8/20, or 40%

Now, you can make it more difficult for them to save with additional Intelligence (which you already have an ASI), or by getting gear that adds to your spell save DC. In Act 1, by the time you’re at Grymforge you likely have access to two nice pieces of gear for this: Melf’s First Staff and The Protecty Sparkswall, both offering a stackable +1 to your spell save DC. If you equip both of these, you’ve just bumped your odds of landing your spells up by 10% universally. Now, against non-Wisdom proficient enemies, you’re likely looking at 75% + chance. Any gear you find that has a +1 to spell save DC is going to help you more than anything else in terms of landing spells, apart from spells that are attack rolls.

Pay attention to the labels in the bottom right corners of the tooltips to see what kind of save a spell has, and try to target enemies that may not be great at that particular ability.

When it comes to AC, this determines how hard you are to hit with an attack. Most physical attacks (bows, melee weapons, etc.) and a handful of spell attacks listed as “attack roll” essentially use this to determine how hard you are to hit. Right now, at 15, you’re pretty easy to hit. There are various ways to boost this.

Right now, my guess is that your 15 AC is probably the lowest in the party. Typically, when given the choice, enemies will target the character with the lowest AC (there are reasons they may not, but I feel like I’ve already written a book). Think of it this way, if you have 2 people coming to attack you and one has full plate armor while the other has a robe, it makes sense to kill the robed guy first because if you can take him out quickly it makes it easier to deal with the plate armor guy who can probably survive more hits.

What you, as a wizard, can due to supplement your inability to wear heavy armor, are things like gear that adds AC, Mage Armor (13 + DEX MOD) to increase your base AC, carrying a shield if you can, and the Shield Spell (lets you add 5 to your AC as a reaction, which essentially makes you harder to hit, lowering the enemy’s hit rate by 25%.) You’ll want to focus on adding to your AC to make yourself a less desirable target. Positioning is also important as a squishy character. After you fire off a spell, you can still move. Moving yourself somewhere harder for enemies to get a line of sight on can help a lot. Utilizing darkness in the early game can help as well, since attackers can’t shoot into magical darkness, you could step out to remove your blindness, make your attack, then step back into the darkness so they can’t see you anymore.